P0420

DTC P0420

DTC DESCRIPTOR

DTC P0420
Catalyst System Low Efficiency

DIAGNOSTIC FAULT INFORMATION
Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into CO2, and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. The control module monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific idle conditions. The control module compares the engine and catalyst oxygen sensor signals in order to determine if the oxygen storage capacity of the catalyst is degraded.

IMPORTANT: A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

If the ECM detects the degraded condition DTC P0420 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0030, P0036, P0068, P0069, P0097, P0098, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0120, P0121, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0171, P0172, P0220, P0300, P0315, P0335, P0336, P0340, P0341, P0442, P0443, P0446, P0449, P0452, P0453, P0461, P0496, P0502, P0503, P0506, P0507, P1133, P1516, P1681, P2135, P2176 are not set.
- The engine has been running for more than 10 minutes.
- The engine speed is within 200 RPM of the desired idle.
- The engine coolant temperature (ECT) is between 50-125°C (122-257°F).
- The barometric pressure (BARO) is more than 70 kPa.
- The TWC calculated temperature is between 550-765°C (1,022-1,409°F).
- The vehicle is in Closed Loop.
- The intake air temperature (IAT) is between -20 and +80°C (-4 and +176°F).
- The battery voltage is more than 9 volts.
- The throttle position (TP) is 1.5 percent or less.
- The short term fuel trim (FT) is between -10 and +10 percent.
- This diagnostic attempts one test during each valid idle period, when the above conditions have been met for 1 minute. This diagnostic attempts up to 6 tests during each drive cycle.

CONDITIONS FOR SETTING THE DTC
- The control module determines that the efficiency of the catalyst has degraded below a calibrated threshold.
- This diagnostic may conclude in as few as one test attempt. However, this diagnostic may require as many as 18 test attempts, which would require at least 3 drive cycles. Each test attempt may conclude within approximately 7 minutes.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- Inspect for the following conditions, which may cause a catalytic converter to degrade:
- An engine misfire
- High engine oil or high coolant consumption
- Retarded spark timing
- A weak or poor spark
- A lean fuel mixture
- A rich fuel mixture
- A damaged oxygen sensor or wiring harness
- The catalyst test may abort if the vehicle falls outside the conditions for running the DTC.
- A catalyst may be temporarily degraded if a fuel with high sulfur content has been used. Drive the vehicle at highway speeds for 10 minutes and retest the converter.
- If an intermittent condition cannot be duplicated, the information included in the Freeze Frame Records can be useful in determining the vehicle operating conditions when the DTC was set.
- If the condition is determined to be intermittent, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

CIRCUIT/SYSTEM VERIFICATION
Operate the vehicle within the Conditions for Running the DTC.
- If the DTC fails this key cycle, proceed with Circuit/System Testing.

CIRCUIT/SYSTEM TESTING

NOTE:
- Refer to Three-Way Catalytic Converter Damage Notice.
- Refer to Heated Oxygen Sensor (HO2S) Resistance Learn Reset Notice.

IMPORTANT: A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

1. Inspect the catalytic converter for the following conditions:
- Dents
- A severe discoloration caused by excessive temperatures
- Road damage
- An internal rattle caused by damaged catalyst substrate
- Restrictions
- If a condition is found, replace the catalytic converter.
2. Inspect the exhaust system for the following conditions:
- Leaks
- Physical damage
- Loose or missing hardware
- Properly torqued HO2S
- If a condition is found, repair the exhaust system.
3. Inspect the HO2S 2 for the following conditions:
- A grounded wiring harness
- Damage
- If a condition is found, replace the HO2S 2.
- If no physical condition is detected, replace the catalytic converter.

REPAIR INSTRUCTIONS

IMPORTANT: A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
- Catalytic Converter Replacement (RPO LE5) Catalytic Converter Replacement (RPO LSJ) Catalytic Converter Replacement (RPO L61)
- Heated Oxygen Sensor Replacement - Position 2
- Exhaust Leakage
- Restricted Exhaust

REPAIR VERIFICATION
1. Operate the vehicle within the Conditions for Running the DTC.
2. Verify if DTC P0420 has passed or failed this ignition cycle with the scan tool.
3. If 6 tests have been attempted and the DTC has not run or passed during this key cycle, turn the key to OFF for 30 seconds, then run the test a second time.
4. A maximum of 12 tests per key cycle will run if each test is a combination of passed, failed, or aborted tests.
5. After a code clear, the catalyst test will run once if the test is a pass.

IMPORTANT: DO NOT touch the accelerator, the HVAC, or the steering wheel while a catalyst test is in progress.

6. Allow the engine to return to a stabilized idle. Keep the vehicle in DRIVE.